This invention relates to methods of making a firearm ammunition projectile from metal powders. xe2x80x9cPowder-basedxe2x80x9d as used herein refers to projectiles comprising metal powders as opposed to shaped solid metal or metal alloys, the latter being excluded as a part of the present invention.
xe2x80x9cGreenxe2x80x9d firearm ammunition projectiles generally comprise projectiles which do not include lead as a component of the projectile. In recent years lead has been identified as a xe2x80x9cpollutantxe2x80x9d and has been banned from much of the firearm ammunition projectiles. As a substitute for lead projectiles, projectiles formed from a combination of various metals, particularly, metal powders, have been developed. Commonly, tungsten metal powder is mixed with tin, zinc, bismuth, or other metal powder, the mixture is die-formed into individual cores which are subsequently loaded into a metal jacket. The leading end of the metal jacket, containing one or more cores is closed by defining an ogive on such leading end.
One major problem with powder-based (i.e. non-lead containing) projectiles relates to the non-uniformity of the density distribution of the powders which go to make up the projectile. First, it is to be noted that powder-based projectiles desirably provide at least the same performance when fired to a target as do lead projectiles, and, in certain instances, produce like recoil values when the projectile is fired from a weapon. Second, non-uniformity of density of the projectile, at least about the longitudinal centerline of the projectile, (a) reduces the accuracy of delivery of the projectile to a target, (b) reduces the ballistics coefficient of the projectile, (c) imparts nutation to the fired projectile thereby limiting its range of travel from a firearm, among other things. This problem of non-uniformity of density of the core and/or the resultant projectile, is exacerbated when using two or more metal powders, of different densities, in a mixture thereof, for forming a projectile. More specifically, for example, mixtures of tungsten powder and tin, zinc, bismuth or like metal powder, for example, tend to separate, by gravity, into layers of the relative heavy tungsten powder and of the relatively lighter metal powder, by reason of the difference in their respective densities. Such separation may occur in the course of mixing the metal powders together, in transferring of portions of the mixture between containers, in transferring of portions (aliquots) of the mixture into a die, in movement of the mixture from location to location or even during storage (i.e., any vibration of the mixture) and/or in the course of die-forming of the portions of the metal powders into a core which is subsequently encapsulated in a metal, e.g. copper, jacket.
Bare, i.e. non-jacketed, projectiles containing tungsten powder are unacceptable for use in small-bore weapons, particularly those weapons having rifled barrels. The exposed tungsten powder in the non-jacketed projectile is severely abrasive and quickly erodes and renders ineffective the barrel of the weapon. Moreover, individual particles of the tungsten tend to break away from the projectile and enter the mechanism of the weapon, again rendering the weapon ineffective, and often completely useless. This latter factor is particularly a problem with semi-automatic and/or automatic weapons in that the tungsten particles migrate into the bolt-actuating mechanism of these weapons to the extent that the weapon fails to function.
In the course of loading a die-formed core into a metal jacket, it is commonly required that the core be pressed into the jacket to ensure complete filling of the jacket by the core. Also, it is common to die-form an ogive on the leading end of the jacket and core container therein. Each of these manufacturing operations tends to disrupt the powder-based core and further at least partially destroy whatever uniformity of density the core may have at the time it is removed from its forming die.
It is an object, therefore, of the present invention to provide a method of making a firearm ammunition projectile employing a mixture of relatively heavy and relatively light metal powders which are substantially uniformly distributed through the projectile.